Improve detection logic for log list

Attempt to better detect when the log lists are ready. The use of
FileObserver for the current file hierarchy introduces multiple race
conditions. Simply try to access the "current" subdirectories at regular
intervals to confirm the readiness of the log lists.

Bug: 416579133
Test: atest --iterations 100 NetSecConfigCertificateTransparencySctLogListTestCases
Flag: EXEMPT bugfix
Change-Id: I02335f92b272757714473eae0174e4d14a651f25